Method of making a laminated container wall structure

ABSTRACT

A method of manufacturing a laminated metal container wall having an integral opening device. Providing a metal sheet, coating the sheet with an adhesive selected from the group consisting of epoxy, polyester and polyurethane and subsequently securing to the sheet by means of the adhesive a continuous layer of barrier material selected from the group consisting of lowdensity polyethylene, high-density polyethylene and cast polypropylene. Subsequently scoring said sheet to define a severable and/or removable sector and leaving residual metal along the score line of a thickness of about 0.002 to 0.006 inch. Effecting the scoring while preserving the integrity of the barrier by maintaining continuity of the layer of barrier material. Simultaneously with the scoring operation reducing the thickness of the barrier material in the regions underlying the scoring through compressibly established flow without penetrating entirely through the layer. This compressibly established flow serves to reduce the shear resistance to severance of the barrier when the laminated container wall is opened. An outer protective material selected from the group consisting of a polyester, polyvinylidene chloride, polyvinyl chloride and medium- or highdensity polyethylene may be continuously secured to the barrier material. A laminated metal container wall made by the above method having a barrier material thickness of about 0.002 to 0.003 inch in the portion not underlying the score line and a reduced thickness in the portion underlying the score line. The barrier material having a continuous panel covering structure. An outer protective material selected from the medium- consisting of a polyester, polyvinylidene chloride, polyvinyl chloride and medium- or highdensity polyethylene secured to the barrier material.

United States Patent [72] Inventors Herbert Gayner Monroeville, Pa.;John N. Demsey, Jr., Oakland, Calif. [21] Appl. No. 825,164 [22] FiledMay 16, 1969 [45] Patented Jan. 4, 1972 [73] Assignee Aluminum Companyof America Pittsburgh, Pa.

[54] METHOD OF MAKING A LAMINATED CONTAINER WALL STRUCTURE 7 Claims, 5Drawing Figs.

[52] U.S. Cl 156/257, 220/53 [51] Int. Cl 1332b 31/20 [50] Field ofSearch 220/53; 156/257; 156/330; 113/80 DA, 15 A, 120 Q, 121 AC [56]References Cited UNITED STATES PATENTS 3,251,503 5/1966 Bozek 220/542,978,140 4/1961 Walsh.... 220/53 X 3,358,873 12/1967 Gelber 220/533,380,622 4/1968 Garavaglia et al. 220/53 3,389,827 6/1968 Abere et a1.220/53 3,475,240 10/1969 Manaka et al. 156/330 X 3,481,813 12/1969Wiggers 156/257 Primary Examiner-Benjamin A. Borchelt AssistantExaminer-Daniel A. Bent AttorneyAmold B. Silverman ABSTRACT: A method ofmanufacturing a laminated metal container wall having an integralopening device. Providing a metal sheet, coating the sheet with anadhesive selected from the group consisting of epoxy, polyester andpolyurethane and subsequently securing to the sheet by means of theadhesive a continuous layer of barrier material selected from the groupconsisting of low-density polyethylene, high-density polyethylene andcast polypropylene. Subsequently scoring said sheet to define aseverable and/or removable sector and leaving residual metal along thescore line of a thickness of about 0.002 to 0.006 inch. Effecting thescoring while preserving the integrity of the barrier by maintainingcontinuity of the layer of barrier material. Simultaneously with thescoring operati n reducing the thickness of the barrier material in theregions underlying the scoring through compressibly established flowwithout penetrating entirely through the layer. This compressiblyestablished flow serves to reduce the shear resistance to severance ofthe barrier when the laminated container wall is opened. An outerprotective material selected from the group consisting of a polyester,polyvinylidene chloride, polyvinyl chloride and mediumor high-densitypolyethylene may be continuously secured to the barrier material.

A laminated metal container wall made by the above method having abarrier material thickness of about 0.002 to 0.003 inch in the portionnot underlying the score line and a reduced thickness in the portionunderlying the score line. The barrier material having a continuouspanel covering structure. An outer protective material selected from themediumconsisting of a polyester, polyvinylidene chloride, polyvinylchloride and mediumor high-density polyethylene secured to the barriermaterial.

METHOD OF MAKING A LAMINATED CONTAINER WALL STRUCTURE BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to alaminated metal container wall having an integral opening deviceprovided with a scored removable sector and the product manufacturedthereby. In addition and more specifically, this invention relates tothe method of manufacturing a metal container wall without destroying aprotective barrier continuously adhesively bonded to the wall.

2. Description of the Prior Art Containers having a metal container wallprovided with an integral opening device which eliminates the need forthe use of a separate opener to gain access to the container contentshave long been known and used commercially. One of the preferred formsof opening devices found frequently in container walls, such as jar andbottle closures and can ends, has a removable sector defined within ametal panel portion which has been weakened by scoring part way but notcompletely through the panel. An operating member, which is frequentlyin a form of a lever providing a mechanical advantage, is secured to theremovable sector. In gaining access to the contents of the container,the consumer merely employs the operating lever to sever the removablesector from the container wall.

In the conventional commercial method of manufacturing sheet for suchcontainer walls, the metal sheet is coated on both sides with asolvent-based organic coating. The sheet is then heated to asufficiently high temperature to evaporate the solvent and cure thecoating. Container wall blanks are then severed from the sheet andformed into container walls. These container walls are subsequentlyconverted to provide integral easy opening devices.

The end or closure panel is scored by the impact force of an indentertool. During this process the container wall is supported upon agenerally fiat anvil surface. As a result of the tremendous forces whichare applied to the end wall during forming, the coating on the panelundersurface is fractured. Were the wall to be used in this condition,this fractured coating would permit the container contents which arefrequently potentially corrosive to contact the exposed metal and attackthe same. With respect to food, many products are particularlytroublesome. For obvious reasons, food packers desire a single containersystem suitable for use for a full product line regardless of varyingchemical properties among different products. Also, should the end wallbe made of a different material than the can body, as is the case wherean aluminum end is placed upon a tin plate can, the aluminum mightfunction asa sacrificial anode and corrode.

As a result of this substantial corrosion hazard it is found necessaryin commercial practice to place a repair coating upon the undersurfaceof the container wall after scoring has been completed. This, of course,requires additional handling of the can end, the use of additionalequipment, the addition of another process step during manufacture andthe use of additional material.

It has also been suggested to score the metal panel prior to coating theundersurface. This alternative also has significant disadvantages. Ifthe sheet were scored prior to severance of the end wall blanks, therewould be the risk that the score line might be fractured duringsubsequent forming operations. If, on the other hand, each end wall wereto be individually coated after scoring, this would necessitateindividual handling during the coating process. It would also result inthe difficulty of providing a continuous uniform coating to theirregularly shaped end wall.

SUMMARY OF THE INVENTION This invention has solved the above enumeratedproblems by providing a method of manufacture and structure for a scoredcontainer wall having an integral opening device. The metal sheet isprotectively covered by a continuous adhesively bonded thermoplasticbarrier material which will be reformed but not fractured responsive tothe substantial compressive force applied by the scoring tools. Thebarrier material will remain continuous throughout the scoring operationand thereafter. It also will have such a thickness as to provide aneffective protective barrier between the undersurface of the containerwall and the container contents during storage.

In the method of this invention a film of barrier material iscontinuously adhesively secured to the undersurface of the metalcontainer wall. The adhesive is selected from the group consisting ofepoxy, polyester and polyurethane. The barrier material is selected fromthe group consisting of low density polyethylene, high densitypolyethylene and cast polypropylene. After manufacture of the laminate,the metal is subsequently scored, either before or after severance ofcontair-er wall blanks from the sheet. Scoring is effected to such adepth as to leave a metal residual along the score line of about 0.002to 0.006 inch (2 to 6 mils). During the scoring operation, the thicknessof the film of barrier material is reduced in the region underlying thescore line as a result of the flow of barrier material responsive to thecompressive force.

In one form, the barrier material has a thickness of about 0.002 to0.003 inch. An outer protective material selected from the groupconsisting of a polyester, polyvinylidene chloride, polyvinyl chlorideand medium or high density polyethylene is secured to the barriermaterial. This may be laminated to the barrier material by directadhesion or secured thereto by means of an independent adhesive. Wherean independent adhesive is employed, this second adhesive is selectedfrom the group consisting of epoxy, polyester and polyurethane. Theproduct of the above method may have a metal panel with a thickness inthe unscored portion from about 0.008 to 0.0145 inch and a narrow rangeof residual metal thickness of about 0.0025 to 0.0045 inch in the scoredportions.

It is an object of this invention to provide a method of manufacturing alaminated container wall with a continuously adhesively bonded barriermaterial secured to the underside of a metal panel or sheet in suchfashion as to resist destruction of continuity of the protective barrierwhen the laminate is subjected to the substantial force encounteredduring scoring of the metal panel.

It is another object of this invention to provide a laminated containerwall having a scored integral opening device wherein the score line isof substantial depth and a substantial score residual remains with acontinuous corrosion resistant barrier adhesively bonded to the metalundersurface and of sufficient thickness to resist corrosive attack onthe metal by the container contents during storage.

It is another object of this invention to provide a barrier composed ofone or more corrosion resistant materials laminated to the metal panelin sufficient thickness to resist film fracture and adhesive failureduring both score line formation and subsequent storage of a filledcontainer to which it is secured.

It is yet another object of this invention to provide such a containerwall structure simply and economically without the need for any repaircoating to the container wall undersurface after the scoring operation.

These and other objects of this invention will be more fully understoodand appreciated from the following detailed description of theinvention, on reference to the illustrations appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary sectionalelevation of one form of sheet laminate of this invention.

FIG. 2 is similar to FIG. I but shows a modified form of laminatecontemplated by this invention.

FIG. 3 illustrates a fragmentary sectional elevation of a can end ofthis invention showing the scoring tools in position prior to theinitiation of scoring.

H68. 4 and 5 are enlarged sectional elevations showing a portion of FIG.3 during the intermediate and final stages of score line formation,respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more specifically tothe drawings, FIG. 1 illustrates a metal sheet 2 to which there iscontinuously bonded a layer of barrier material 4, which is preferablyin the form of a film. Bonding is effected through a coating of adhesivematerial 6. The metal sheet 2 may be any material suitable for use in acontainer wall, be it a can end or closure. Aluminum and tin platedsteel are suitable for such purposes.

As used herein the terms container wall" and container end wall" will beemployed as a convenient means of generically referring to variousstructural container portions having integral devices for assistingseverance and/or removal of at least a portion thereof to permit accessto the container contents. Closures for jars and bottles and can endsare among the specific forms contemplated by the use of these terms.

The barrier material 4 must be carefully selected, as it must havesufficient mechanical strength to resist destruction or excessivethinning during the application of the substantial force applied by thescoring tools. Among the materials found to be suitable for suchpurposes are polyethylene and cast polypropylene. The material ispreferably provided in the form of a film having a thickness of 0.002 to0.003 inch (2 to 3 mils) and is continuously bonded to the metal sheetby means of the adhesive material 6.

With respect to polyethylene density, polyethylene of differentdensities can perform effectively, with a preference of one, within thelimitations specified herein, being based primarily upon the nature ofthe specific product to be stored in the container. As used herein. lowdensity polyethylene means a polyethylene material having a density ofabout 0.9l to 0.925, "medium density polyethylene" means a polyethylenematerial having a density of about 0.926 to 0.941 and Thigh densitypolyethylene means a polyethylene material having a density of about0.942 to 0.965. It has been found that the high density polyethyleneprovides a more effective barrier with respect to preventing corrosiveproduct contact with the metal undersurface. The low densitypolyethylene exhibits better mechanical strength with respect to thecompressive impact of the scoring tools and also exhibits better bondingproperties with respect to the metal end wall. The medium densitypolyethylene exhibits barrier, compressive and bonding propertiesintermediate the high and low density polyethylene.

it is important that the adhesive 6 be carefully selected in order toprovide continuous bonding between the metal sheet 2 and the barriermaterial 4. The adhesive must maintain the strength of bond during thescoring operation. In this respect it is noted that the undersurface ofthe metal sheet 2 is generally deformed slightly downwardly during thescoring operation (FIG. 5). The adhesive bond continuity must survivethe sub stantial compressive forces employed to establish thisdeformation, as well as the compressive forces applied during physicaldislocation produced by this displacement. In addition, the adhesivemust after having been subjected to the scoring operation exhibitcontinued strength of bond during the period of storage of the sealedcontainer.

The adhesives which are preferred for purposes of this invention areepoxy, polyurethane and polyester adhesives. A suitable epoxy adhesiveis that sold under the trade name Shell ADX57B and a suitablepolyurethane adhesive is that sold under the trade name Adcote 102.These adhesives are applied in coating form in quantities of about 1.0to 5.0 mg./sq. in. and preferably about 1.0 to 3.0 mg./sq. in. In orderto obtain the maximum intimacy of bond, it is preferable to cure theadhesive. This may be accomplished by heating at a temperature of 150 to475 F. for a period of about 10 to 60 minutes. Such heating mayconveniently be effected either during lamination, as by means of a hotnip or subsequent thereto. In addition, with respect to some adhesives,it may be desirable to add a relatively small quantity of a catalystfrequently used for the particular adhesive in a conventional fashion.

Another form of sheet structure contemplated by this invention isillustrated in FIG. 2. In this FlG., the barrier member 4 is laminatedto one surface of a metal sheet by means of an adhesive 6. An outerprotective member 10, which is preferably in the form of a film, iscontinuously bonded to the exposed surface 12 of barrier member 4 bymeans of an adhesive M. The adhesive 14 is preferably selected from thegroup consisting of epoxy, polyurethane and polyester and applied as acoating in quantities of about i .0 to 5.0 mg./sq. in., preferably about1.0 to 3.0 mgJsq. in.

if desired, the adhesive 14 may be eliminated and outer protectivemember 10 may be directly bonded to barrier member 4 by means of directlamination without an independent adhesive. This may be accomplishedeither prior to or after securance of barrier member 4 to metal sheet 2,although securance prior will generally be more convenient.

The form of laminated material illustrated in FIG. 2 provides astructure having increased mechanical strength and barrier propertieswith respect to that form illustrated in FIG. 1. The outer protectivemember 10 preferably has a thickness of about 0.00025 to 0.001 inch. Thebarrier member 4 being substantially thicker than outer protectivemember 10 provides a ply of increased compressibility which will absorba greater proportion of the compressive scoring force throughcompressive deformation and ultimate flow than the outer protectivemember. The outer protective material 10 is preferably composed of apolyester such as polyethylene teraphthalate resin, polyvinylidenechloride, polyvinyl chloride or a medium or high density polyethylene. Asuitable polyester is that sold under the trade name Mylar. A suitablepolyvinylidene chloride is that sold under the trade name Saran.

The polyesters exhibit extreme resistance to fracture which providesmarked improvement in the mechanical properties of the laminate inresisting the compressive force encountered in scoring. Polyvinylidenechloride exhibits extremely high resistance to penetration bypotentially corrosive materials such as acids.

In the method of this invention, after manufacturing the laminated metalsheet, scoring may be effected either while the sheet is intact or afterindividual container wall blanks have been severed from the sheet. Incommercial practice, it is frequently preferable to score after thecontainer wall blanks have been severed from the sheet and after theclosures have been formed. For convenience of reference, referenceherein to scoring sheet" will contemplate scoring either a full sheet ora container wall or container wall blank which is a smaller sheetlikeelement.

As is shown in FIGS. 3, 4 and 5, scoring may be effected by a truncatedindenter tool 20 which latter two provide positioned above the laminatedcontainer wall 22 and an anvil 24 which is in supporting underlyingposition with respect to the laminated end wall 22. in effecting scoringon a commercial scale with automatic equipment, the end wall 22 isreceived on the anvil 24 and the indenter tool 20 is rapidly broughtdownwardly to provide forceful impact with the metal panel 26 portion ofthe end wall 22. Depending upon the specific configuration of theindenter tool, the establishment of the score line may result eitherfrom severance and physical displacement of the metal or extruded metalflow or both.

With respect to aluminum container end walls, the metal panel 26frequently has a thickness of about 0.008 to 0.0145 inch. Scoring insuch walls is effected in such fashion as to leave a metal residualthickness in the score line of about 0.002 to 0.006 inch and generallyabout 0.0025 to 0.0045 inch. In order to effect such a reduction andmaintain commercially acceptable speeds of production, the force withwhich the scoring tool 20 engages the metal panel 26 is such thatpressures in the score line region frequently reach the range of 100,000to 300,000 pounds per square inch. It is this substantial impact whichthe laminated protective barrier structure of this invention must resistin order to permit the manufacture of easy open container walls of thistype without necessitating repair coating in order to ensure effectivecorrosion protection and durable adhesive bonding. The problem withrespect to the amount of force which the barrier materials mustwithstand becomes particularly acute with respect to certain aluminumalloys which are frequently employed commercially in the extra hard Hi9temper. The thickness of the sheet, the nature of the alloy and thetemper all may contribute to increased strength requirements of thebarrier materials if they are to function effectively for the purposeintended herein.

In the form illustrated in FIGS. 3 through 5, the indenter tool 20 isinitially positioned above the top surface 28 of metal panel 26. In theform shown inFlG. 4 (a gap being provided between the indenter tool 20and panel 26 for clarity of illustration), the score line 30 has beenpartially formed. Completion of the score line has been effected in theform shown in FIG. 5.

It is noted, as is seen in FIGS. 4 and 5, that a downwardly directedextension 32 of the metal panel 26 is disposed in underlying positionwith respect to the score line 30. Also, the total thickness of thebarrier material 4 and outer protective member has been subjected tothinning in the region underlying score line 30. This thinning occurs asa result of flow, transverse with respect to the score line, establishedin barrier material 4 and/or the outer protective member 10 due to thesubstantial compressive force applied by indenter tool in cooperationwith supporting anvil 24. The total thinning of the barrier material 4,the adhesive coatings and the outer protective material within theportions underlying the score line is about 10 to 50 percent of theiroriginal total thickness and preferably about 10 to 20 percent.

It is noted, however, that the thinning was not sufiicient to produceany openings in material 4 and member 10 which would permitcommunication between lower surface 34 of metal panel 26 and anycontainer contents which are positioned on the opposite side of thebarrier material. It is also preferable that the thinning not besufficient as to substantially impair the barrier properties of thebarrier materials to the point where damaging penetration of thematerials by the container contents can occur.

It will, therefore, be appreciated that the container wall structure ofthis invention is such that the metal panel 26 has been weakened, butnot lanced, to provide a severable and/or removable sector. Prior toopening, the panel 26 remains continuous and serves as a physicalbarrier to the entry of external materials into the container. Whetherthe weakened sector is removable or not, the score line will be severedin effecting access to the container interior. The term removable sectoras used herein shall refer to panel structures which require score lineseverance to gain access to the container interior regardless of whetherthe weakened sector is actually removed from the panel.

The barrier material 4 and the outer protective member 10 serve toprevent potentially corrosive contact between the container contents andthe undersurface 34 of the metal panel 26. In the form illustrated, thebarrier material 4 and outer protective member 10 are continuously andeffectively bonded to each other and to the metal panel 26 by means ofadhesives 6, 14. The integrity of the barrier materials 4, 10 alsoprevents the container contents from reducing the bond of adhesive 6 bycorroding the metal to which it is secured and thus exposing additionalmetal and permitting progressive corrosion over a substantial portion ofthe entire lower surface 24.

In numerous easy open containers of this type, a rigid lever pull tab issecured within the removable sector by appropriate fastening means suchas by an integrally formed rivet. This presents no additional problemswithrespect to maintaining the integrity of the barrier members of thisinvention, as the mechanical demands of such formation are substantiallyless than those encountered with respect to scoring.

It will be appreciated that the adhesive coatings 6,14 while generallysubstantially thinner than barrier material 4 and outer protectivemember 10 may nevertheless-contribute to the total barrier resistance topenetration of potentially corrosion producing materials to the lowersurface 34 of metal panel 26.

Several tests were performed in order to verify the effectiveness of thebarrier of this laminatedmaterial.

EXAMPLE 1 Ten sheets of an aluminum base magnesium alloy (5052')in theextra hard H19 temper having a sheet thickness-of about 0.010 inch werecoated on one side with a' clear epoxy amine coating in the amount of 3mg./sq. in. The reverse side of these sheets was coated with apolyurethane adhesive in-the amount of l mg.,sq. in. Thepolyurethane-adhesive was dried at 250 F. for 2 minutes. Apolyethylene-polyester laminatefilm was then sealed to the panel withthe polyethylene film in contact with the polyurethane adhesive. Thepanels were reheated for 10 minutes at 300 F. and allowed tocool-Circular panel portions were then blanked from the sheet andconverted into 211 diameter can ends. The ends were subsequently scoredin the conventional manner to define a weakened panel sector. No repaircoating was applied. The panel-ends were then compounded with a gasketmaterial and sealed'to cans containing a variety of products includinghydrogenated vegetable oil, liquid vegetable oil, water at 2 l 2 F.,fresh pork-shoulder meat and vegetable juice cocktail. The water andpork were subsequently processed for 45 minutes at 250 F. The vegetablejuice cocktail cans had been filled at an elevated temperature and theremaining cans were filled at room temperature. The packages wereinvestigated after seven daysxExamination of the ends revealed that theundersurface of the metal ends has been maintained free from exposure tothe containercontents. The ends employed with the water sample assumed aslightly clouded color but were otherwise uneffected and no effectwhatsoever was noted with respect to the ends employed with the otherfood products.

EXAMPLE 2 In order to compare the product of conventional practices,several sheets of the same alloy employed in example 1 were coated onboth sides with an epoxy phenolic by means of a solvent which wassubsequently evaporated and the coating cured by heating the panels at400 F. foraperiod of 10 minutes. Circular panel portions were thenblanked from the sheet and converted into 211 diameter can ends. The canends were subsequently scored in the conventional manner to define afrangible panel sector. Careful examination of the scored can endsrevealed fractured portions of the epoxy phenolic coatings which wouldhave required the subsequent application of a repair coating in orderto-produce a commercially acceptable can end.

EXAMPLE 3 Tests were made in order to determine the effectiveness'ofbonding obtained by various adhesives. Alurninu'm can ends having athickness of 0.0105 inch were madefrom 5052-H'19 alloy and were coatedon the outside with a conventional coating in the amount of 3 mg./sq.in. They were converted to easy open can ends by scoring to provide aresidual metal depth of about 0.0045 to 0.005 inch. Thecurledperipheraledges of the ends were compounded with a conventional gasket material.Some of the ends had a film of a laminate of lowtdensitypolyethylene-polyvinylidene chloride-polyethylene (sold under the tradename Saranex PZ2000.2l adhesivelysecured to their underside. Others hada polypropylene film (sold under the trade name Extrudo PP12B) securedto their. underside. Bonding was effected with various adhesives.Catalysts of the type normally employed for these adhesives were used.These ends were secured to 21 1x304 tinplate cans containing tomatosoup. After 18 hours of exposure to the food product,

the ends were observed in order to visually determine the degree ofblistering which is an indication of imperfections in the adhesive bondbetween the film and the aluminum substrate. The best performance witheach type of film was obtained in those samples employing an epoxyadhesive. These samples had no visible blistering with each type offilm. Also yielding superior results were a polyester adhesive and apolyurethane adhesive which yielded only slight visual blistering witheach type of film.

in the method of this invention, a metal sheet is provided with acontinuously bonded film of barrier material which is secured to thesheet by an adhesive coating. The metal sheet is subsequently scored,either as a unit or after it has been severed into smaller metal sheetsor blanks. The scoring is effected to such a depth as to leave residualmetal along the score line of about 0.002 to 0.006 inch in thickness. Asa result of the high impact pressure applied in the score operation, thebarrier material underlying the score line is thinned. As thecompressive force is applied, the barrier material is initiallycompressed and ultimately is caused to flow outwardly away from thescore line. Thus, the metal which maintains its integrity protects thecontents from exposure to foreign materials disposed exteriorly of thecontainer and the barrier materials protect the metal panel fromdamaging contact with the container contents.

In one form of the invention an outer protective film is adhesivelybonded to the barrier material. This film preferably has a thickness ofabout 0.0005 to 0.001 inch. This outer protective material film servesto both strengthen the laminate and increase its barrier properties. Asa result of the effective continuous adhesive bonding of the laminatecoupled with the strength and barrier properties of the barriermaterials, a frangible sector may be scored into the metal panel withoutrequiring repair coating to protect the undersurface of the metal panelwhile in use.

In addition to the foregoing properties, the materials of this inventionhave been so selected that the adhesive bond between the barriermaterial 4 and the undersurface 34 of panel 26 is greater than the shearstrength of the adhesive 6, 1'4 and materials 4, 10. Thus, when thescore line is fractured during opening of the container, this portion ofthe barrier materials will be removed with the sector and therebypresent no obstruction to the free removal of the container contents. Inaddition, the thinning of the barrier materials during scoring furtherreduces the shear resistance to severance of these materials whenopening the container.

Commercial requirements make it extremely desirable to provide a singletype of container end wall for use with a broad range of products. Thematerials contacting the products must have no appreciable detrimentalefi'ect thereon. This is particularly true with respect to foodproducts. As is commonly known as result of the variations in chemistryof the food products as well as preservatives, seasoning and otheradditives provide a broad spectrum of chemical materials which arepotentially corrosive with respect to metals. The materials of thisinvention provide an effective barrier with respect to a broad range ofmaterials including those which are particularly troublesome such asfresh pork shoulder meat, vegetable juice cocktail and tomato soup (Seeexamples 1 and 3). Also, these materials are compatible with foodproducts and produce no damaging effect thereon even when stored forextended periods of time.

The method and product of this invention, therefore, are uniquely suitedto providing a protective barrier coating which will serve to preventcorrosion, both through food attack and through one of the materialsacting as a sacrificial anode during usein a container. The materialsalso provide a laminate structure of such strength that the barrierproperties are not destroyed by the strong impact force encounteredduring commercial scoring operations. This is true even with respect tohard temper materials. in addition, the laminate may advantageouslybe-formed while the metal is in sheet form. it requires no specialhandling during normal container end wall manufacture, scoring andsealing. All of this is economically effected without the need forexpensive materials or a substantial capital investment in newequipment.

Whereas particular embodiments of the invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details may be made withoutdeparting from the invention as described in the appended claims.

We claim:

1. A method of manufacturing a laminated metal container wall having anintegral opening device, comprising providing a metal sheet having acontinuous portion to be converted to said container wall,

providing on said metal sheet a layer of an adhesive selected from thegroup consisting of epoxy, polyester and polyurethane, securing to saidmetal sheet by means of said adhesive layer a continuous layer ofbarrier material selected from the group consisting of polyethylene andcast polypropylene,

subsequently scoring said continuous portion of said metal sheet todefine a removable sector therein,

effecting said scoring while preserving the integrity of said barrier bymaintaining continuity of said layer of said barrier material,

said scoring of said continuous portion of said sheet being effected tosuch a depth as to leave residual metal along all of said score line andsaid residual metal having a depth of about 0.002 to 0.006 inch, and

simultaneously with said scoring reducing the thickness of said layer ofbarrier material in the regions immediately underlying said scoringwithout penetrating entirely through said layer by compressiblyestablished flow to reduce the shear resistance to severance of saidadhesively secured layer of barrier material when said laminatedcontainer wall is opened, whereby said metal sheet panel will have aweakened removable sector with an adhesively bonded underlyingcoextensive barrier material secured thereto.

2. The method of claim 1 including said barrier material is selectedfrom the group consisting of low density polyethylene, high densitypolyethylene and cast polypropylene,

providing said layer of barrier material continuously over at least thatportion of said container wall which will be directly exposed to thecontainer interior, applying said adhesive layer as a substantiallycontinuous coating at about 1.0 to 5.0 mg.lsq. in.,

applying said barrier material in the form of a film having a thicknessof about 0.002 to 0.003 inch, and

adhesively securing to said barrier material an outer protectivematerial selected from the group consisting of a polyester,polyvinylidene chloride, polyvinyl chloride, high density polyethyleneand medium density polyethylene.

3. The method of claim 2 including said outer protective material is asubstantially continuous film secured to said barrier member by means ofa second adhesive selected from the group consisting of epoxy, polyesterand polyurethane, and

said second adhesive applied as a coating in the amount of about 1.0 to5.0 mg.lsq. in.

4. The method of claim 2 including said barrier material and said outerprotective material each being a film,

said adhesive coatings of substantially uniform thickness andestablishing continuous bonds, and

said protective material film having a thickness of about 0.00025 to0.001 inch.

5. The method of claim 2 including after establishing said laminate butprior to scoring, severing can end blanks from said sheet, and

subsequently scoring said blanks without any subsequent application of arepair coating to protectively cover the undersurface of said scoring.

6 The method of claim including said metal sheet is aluminum, prior toadhesively bonding said barrier material to said metal sheet said outerprotective material is secured to said barrier material, 5 effectingsaid scoring by means of a generally V-shaped indenter tool whichengages the top surface of said can end blanks and a generally flatsupporting anvil which contacts the outer protective material, andduring said scoring operation the reduction in total 10 thickness ofsaid barrier material, said adhesive coatings and said outer protectivematerial within the portions thereof underlying said score line is aboutl0 to 50 percent of said original total thickness.

7. The method of claim 5 including after establishing said laminate butprior to scoring, heating said laminate to a temperature of about l50 to475 F. for a period of about 10 to 60 minutes to establish a uniformlybonded continuous protective barrier structure.

i i Q l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,632,461 Dated January 4, 1972 Inventor(s) Herbert Gayner and John N.Demsey It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Delete the second paragraph of the Second paragraph of Abstract AbstractAfter "which" delete "is" and insert Col. 4, line 51 -latter twoprovide--.

After "which" delete "latter two Col. 4, line 54 provide" and insert--is-.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.FLBTCHER,JR.

Commissionerof Patents Attesting Officer DRM P0405" USCOMM-DC 60376-P69h v.5. GOVERNMENT PRlNTlNG OFFICE I 969 O366-334

2. The method of claim 1 including said barrier material is selectedfrom the group consisting of low density polyethylene, high densitypolyethylene and cast polypropylene, providing said layer of barriermaterial continuously over at least that portion of said container wallwhich will be directly exposed to the container interior, applying saidadhesive layer as a substantially continuous coating at about 1.0 to 5.0mg./sq. in., applying said barrier material in the form of a film havinga thickness of about 0.002 to 0.003 inch, and adhesively securing tosaid barrier material an outer protective material selected from thegroup consisting of a polyester, polyvinylidene chloride, polyvinylchloride, high density polyethylene and medium density polyethylene. 3.The method of claim 2 including said outer protective material is asubstantially continuous film secured to said barrier member by means ofa second adhesive selected from the group consisting of epoxy, polyesterand polyurethane, and said second adhesive applied as a coating in theamount of about 1.0 to 5.0 mg./sq. in.
 4. The method of claim 2including said barrier material and said outer protective material eachbeing a film, said adhesive coatings of substantially uniform thicknessand establishing continuous bonds, and said protective material filmhaving a thickness of about 0.00025 to 0.001 inch.
 5. The method ofclaim 2 including after establishing said laminate but prior to scoring,severing can end blanks from said sheet, and subsequently scoring saidblanks without any subsequent application of a repair coating toprotectively cover the undersurface of said scoring.
 6. The method ofclaim 5 including said metal sheet is aluminum, prior to adhesivelybonding said barrier material to said metal sheet said outer protectivematerial is secured to said barrier material, effecting said scoring bymeans of a generally V-shaped indenter tool which engages the topsurface of Said can end blanks and a generally flat supporting anvilwhich contacts the outer protective material, and during said scoringoperation the reduction in total thickness of said barrier material,said adhesive coatings and said outer protective material within theportions thereof underlying said score line is about 10 to 50 percent ofsaid original total thickness.
 7. The method of claim 5 including afterestablishing said laminate but prior to scoring, heating said laminateto a temperature of about 150* to 475* F. for a period of about 10 to 60minutes to establish a uniformly bonded continuous protective barrierstructure.